I just got a fastfire from the EE and have only played with it a little, I put it on a beretta cx4 carbine; but here is my two cents.
The dot is only 4moa I believe. That is fine except in dim light. The inability to adjust the brightness can make for a hard to find dot. It brightens up great in daylight, not overly bright. In near darkness it flickers, very annoying, may just be the unit I have.
Off topic but for anyone with the beretta it is nice on my storm. Co-witnesses with the factory iron sights perfectly, they fold down when not needed. Glad I bought it, this gun is just a range toy for me and I couldn't justify the cost of an eotech on it.